Nicky Hayden suffered the second retirement of his maiden World Superbike season in Race 2 at Aragon, suffering from brake issues throughout the whole race.
The 34-year-old American finished sixth in the opener, but failed to complete the Sunday race, pulling into the pits while running well down the order.
"It was a bad day - there is not much else to say," said Hayden.
"Everything that could have gone wrong did go wrong: on the sighting lap we started having some problems and on the warm up lap, again, I could feel something was still not right. We had a big vibration at the front end and I could not get my bike stopped.
"I tried to stay out to salvage some points but there was not much I could do. Eventually it got worse, so I chose not to take any unnecessary risks and pulled out of the race.
"It’s the second DNF of the season, which prevented me from getting more experience on the bike, but it is what it is. We have learned something today and we now look forward to the next round."
It was Hayden's second retirement in just six races, as he had to withdraw from the Saturday race at Buriram due to engine issues.
Crash-filled weekend for van der Mark
Following a strong start to the season, fellow Honda rider Michael van der Mark endured a difficult weekend at Aragon.
Having crashed out in both qualifying and the first race, he scored his only points with a seventh place on Sunday.
"The race was more difficult than I expected," said the Dutchman. "We lost some time in the warm up so I could only do a few laps.
"I had a great start and I was able to make up some positions, but I could feel that the bike setup was not working as well as it did in practice.
"I did all that was possible to keep a good pace but in the end I was losing a lot of ground."